Optical properties and carrier localization in the layered phosphide EuCd${}_2$P${}_2$

Abstract

The temperature dependence of the complex optical properties of the layered phosphide material EuCd${}_2$P${}_2$ have been measured over a wide frequency range above and below $T_{\mathrm{N}}\simeq 11.5$ K for light polarized in the $a-b$ planes. At room temperature, the optical conductivity is well described by a weak free-carrier component with a Drude plasma frequency of $\simeq 1100$ cm${}^{-1}$ and a scattering rate of $1/{\tau }_D\simeq 700$ cm${}^{-1}$, with the onset of interband absorptions above $\simeq 2000$ cm${}^{-1}$. Two infrared-active $E_u$ modes are observed at $\simeq$89 and 239 cm${}^{-1}$. As the temperature is reduced the scattering rate decreases and the low-frequency conductivity increases slightly; however, below $\simeq 50$ K the conductivity decreases until at the resistivity maximum at $\simeq 18$ K (just below $2T_{\mathrm{N}}$) the spectral weight associated with free carriers is transferred to a localized excitation at $\simeq 500$ cm${}^{-1}$. Below $T_{\mathrm{N}}$, metallic behavior is recovered. Interestingly, the $E_u$ modes are largely unaffected by these changes, with only the position of the high-frequency mode showing any signs of anomalous behavior. While several scenarios are considered, the prevailing view is that the resistivity maximum and subsequent carrier localization is due to the formation of ferromagnetic domains below $\simeq 2T_{\mathrm{N}}$ that result in spin-polarized clusters due to spin-carrier coupling [1].

8 pages with 6 figures; five pages of supplemental material

References in corpus (5)

• Spin fluctuation induced Weyl semimetal state in the paramagnetic phase of EuCd${}_2$As${}_2$
• A Single Pair of Weyl Fermions in Half-metallic EuCd2As2 Semimetal
• Colossal Magnetoresistance without Mixed Valence in a Layered Phosphide Crystal
• Strong correlation and massive spectral-weight redistribution induced spin density wave in a-Fe1.06Te
• Resonant X-ray scattering study of diffuse magnetic scattering from the topological semimetals EuCd${}_2$As${}_2$ and EuCd${}_2$Sb${}_2$

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• Electronic band reconstruction across the insulator-metal transition in colossal magnetoresistive EuCd2P2
• Carrier-induced transition from antiferromagnetic insulator to ferromagnetic metal in the layered phosphide EuZn${}_2$P${}_2$
• Unusual magnetic and transport properties in the Zintl phase Eu${}_{11}$Zn${}_6$As${}_{12}$
• Recent advances in understanding and manipulating magnetic and electronic properties of Eu$M_2{X}_2$ ($M$ = Zn, Cd; $X$ = P, As)
• CaCd${}_2$P${}_2$: A Visible-Light Absorbing Zintl Phosphide Stable under Photoelectrochemical Water Oxidation
• Spectroscopic signatures of magnetization-induced band renormalization and strong spin-charge-lattice coupling in EuZn${}_2$As${}_2$